1. Field of the Invention
The present invention relates generally to key tops, and more particularly, to a key top which has a dust-proof design and superior sliding action.
2. Description of the Related Art
As well known to those skilled in the art, a key top is a part of each key switch constituting a keyboard. When a key cap of the key switch is pushed down by an operator's finger, the key top attached to the bottom of the key cap is moved down by finger pressure to turn on a contact point of a flexible printed circuit (FPC), thus realizing key-in operation.
A conventional key top is shown in FIG. 1.
In FIG. 1, the reference numeral 1 denotes a key top. The key top 1 is provided to correspond to each key on a keyboard. A key stem 12 extends downward from a central portion of a lower surface of the key top 1. Stoppers 11 are provided at predetermined positions on the lower surface of the key top 1. The reference numeral 2 denotes a housing, and a guide hole 21 is formed at a predetermined position on the housing 2 to guide the key stem 12. The reference numeral 3 denotes a rubber cup, with a protrusion 31 provided on a lower surface of the rubber cup 3. The reference numeral 4 denotes an FPC having at a predetermined position thereof a contact point 41. The reference numeral 5 denotes a frame.
In a key switch constructed as described above, when the key top 1 is depressed by an operator's finger, the key top 1 moves downward while being guided by the guide hole 21. At this time, the key stem 12 moves downward together with the key top 1, thus pressing down the rubber cup 3. Further, the protrusion 31 of the rubber cup 3 pushes down the contact point 41, so that a key is switched to an ON state.
However, the key switch is problematic in that impurities, such as dust, may enter the guide hole 21 for guiding the key stem 12, thus hindering smooth sliding motion of the key stem 12. Also, during operation of a computer, coffee, water or the like may flow into the guide hole 21, with the result that the smooth sliding motion of the key stem 12 may be hindered. Further, when coffee, water or the like flows to the contact point 41, failure of key-in operation occurs.
The key switch has a disadvantage in that noise is generated when the stoppers 11 come into contact with the housing 2 in the course of the downward movement of the key top 1.
In order to overcome the drawbacks, a key switch of FIG. 2 was proposed. The key switch is constructed so that a key stem 12 is surrounded with a hollow rubber cup 3, thus preventing impurities, such as dust, from entering the key switch.
However, the key switch includes a spring 13 made of metal. The spring 13 is mounted to a lower surface of the key stem 12 to press the contact point 41. The key stem 12 integrated with a key top 1 is usually made of resin. Thus, the key switch has a problem in that the spring 13 must be separately manufactured and then mounted to the key stem 12, so that the number of assembly processes is undesirably increased.
A multiple key, such as an enter key or a spacebar, is a key that is obtained by combining two or more key switches with each other. That is, one multiple key uses two or more key stems 12. Further, an operator may not press the exact center of the multiple key. For example, when an end of the multiple key is pushed down, the multiple key is tilted by a rotational moment. Thereby, a key stem 12 which is distant from the pushed end of the multiple key may not smoothly slide in the guide hole 21.
In order to solve the problem, there has been proposed a link bar which is mounted to a predetermined position of the multiple key so as to transmit pressure uniformly. However, this method has a problem in that the number of components is increased, so that additional assembly processes are required.
Further, since one multiple key uses two or more rubber cups, the rubber cups for the multiple key must be separately manufactured in order to make pressing sensation of the multiple key equal to that of a single key. That is, it is inconvenient to reduce the elasticity of two rubber cups used in the multiple key so that the total elasticity of the rubber cups for the multiple key is equal to the elasticity of one rubber cup used in a single key.